The fouling of anion resins has posed a problem that has confronted ion exchange applications since their inception. Humic substances found in surface waters are high molecular weight polyfunctional organic acids (both carboxylic and phenolic) formed from the breakdown of plant and animal materials. In demineralizer operations, the large organic molecules may coat the resin bead, blocking and/or entering the pores of an anion exchange resin. These organics are retained because of a high affinity for the exchange sites and hydrophobic interactions with the polymer backbone of the resin.
Since the diffusion rates of the organics within the resin are usually slower than those of inorganic ions, not all of the bonds linking the organic acids to the resin are broken during the regeneration cycle. This situation results in only partial regeneration of the resin and excessive rinse times following regeneration. In severe cases, the resin may become "irreversibly" fouled. To alleviate these problems, out-of-service brine or brine/caustic cleaning has traditionally been performed. It has also been suggested that sodium hypochlorite may also be used as such a cleaning treatment. However, resin degradation may occur with use of such a strong oxidizing agent.
U.S. Pat. No. 3,748,285 (Wiltsey et al) is directed toward compositions and methods for cleaning ion exchange resins. The cleaning composition comprises (a) from 60-90% water, (b) from about 0.5-4% of an unsubstituted, liquid aliphatic hydrocarbon having from 5 to 10 carbon atoms, and (c) from about 0-10% of a wetting agent selected from the group consisting of sulfated alcohols and sulfonated hydrocarbons and having from 6 to 22 carbon atoms. In addition, an organic compound (d) having the formula: EQU R(OCH.sub.2 CH.sub.2).sub.x OR
is also made part of the treatment. In accordance with the disclosed formula, R is independently selected from the group consisting of H, lower aliphatic radicals of from 1-6 carbon atoms and radicals having the formula ##STR1## where Z is selected from the group consisting of H and aliphatic hydrocarbon radicals of from 4 to 18 carbon atoms and x is an integer of from about 1 to 20. As to specific (d) compounds disclosed, glycol butyl ether and ethoxylated alkyl phenols are preferred. The gist of the reference is directed toward cationic exchange resins in contrast to the present invention which is directed toward anionic exchange resins. Moreover, Wiltsey et al is concerned with cleansing of hydrocarbon oils from the resins. In contrast, the present invention provides a means for cleansing naturally occurring foulants such as humic acids, lignins, tannins, etc. from anionic exchange resins. Indeed, as shown hereinafter, several of the ethoxylated alkyl phenol compounds have been tested in anionic resin cleaning examples and have proven only marginally effective. Moreover, these ethoxylated alkyl phenols are notorious in their propensity to foam, thus causing severe problems if any leak to the boiler.
Other patents which may be noted of interest include U.S. Pat. Nos. 4,153,761 (Marsh) and 3,536,637 (Noll et al).
Accordingly, there remains a need in the art for resin cleaning materials which may effectively cleanse organic foulants from anionic exchange resins without resulting in resin degradation and/or severe foaming problems. These needs are effectively met by utilization of the resin cleaning methods of the present invention.